In order to realize a ubiquitous information network society, allowing the electronic apparatus to have multiple functions, a reduced scale, a high frequency, and a low price are keys. As a technology that meets these demands, a technology of high-density mounting onto a printed substrate is currently attracting people's attention. For example, in portable terminal apparatus, multiple functions such as a digital camera, a one-segment television set, a wireless LAN, infrared communication, and GPS are beginning to be mounted and, as a result thereof, the circuit substrate tends to have a larger scale. In order to achieve scale reduction, it is demanded that the number of various high-frequency components such as ceramic chip capacitors mounted on a substrate surface is reduced and the components are integrated.
A circuit substrate that is currently prevalent is made of an epoxy-based resin material provided at a low price. Allowing the electronic apparatus to have multiple functions, a reduced scale, a high frequency, and a low price can be achieved if a ceramic capacitor having a high dielectric constant can be embedded into a printed substrate mainly containing an epoxy-based resin.
Among many dielectric materials, perovskite-based oxide ceramics such as BaTiO3, (Ba, Sr)TiO3, and Pb(Zr, Ti)O3 have excellent dielectric property (a relative dielectric constant of 200 or more), and studies for applying them to electronic devices such as multilayer capacitors and printed substrates have been carried out from the beginning of 1990s. However, the heat-resistance temperature of an epoxy-based resin substrate is about 300° C., and it has been basically impossible to embed a capacitor using perovskite-based oxide ceramics that need a high temperature of 600° C. or higher in forming.
As one method for evading this problem, there is proposed a method of using a composite material in which ceramic nanoparticles such as BaTiO3 are dispersed in a resin. However, in this case, the dielectric constant of the composite material is as low as about several ten because of the low dielectric constant (10 or less) of the resin, making it difficult to meet the demanded performance corresponding to a high frequency.
In the meantime, there is proposed a technology of producing the substrate itself with ceramics. However, because the temperature needed for forming the substrate is as high as about 1000° C., the process is complex and it has been difficult to lower the costs. Also, because the volume shrinks by about 10% or more during the process, the dimension precision cannot be raised, thereby raising a problem in that the demand for miniaturization cannot be met.
Studies are also eagerly carried out that aim at developing a thin-film capacitor having a large capacitance by producing barium titanate-based thin film (BaTiO3, (Ba, Sr)TiO3 or the like) through a thin-film process such as physical vapor deposition or chemical vapor deposition. However, there is a problem in that, when the film thickness of the barium titanate-based thin film is reduced to a 100 nm level, the dielectric constant lowers, so that a film thickness of about 100 nm has been a limit by which the capacitor can operate stably as an element. In order to develop a large-capacitance capacitor element of next generation, there is a need to develop a novel high dielectric material that realizes a high dielectric constant and a satisfactory insulation property at the same time in a nano-region that enable simultaneous realization of further scale reduction and capacitance enlargement of the elements.